Distillation process



' spt. 1, 1931. J. v. E. DICKSON 1,821,144

DISTILLATION PROCESS Filed Feb. 15, 1923 anoemoz w, M W a.

Patented Sept. 1,1931

UNlTED' s'rn'rss PATENT OFFICE Joan v. n. mcxson, orwooncairr-on-nonson, new masnv, nssmnon we ran mamrconmm, a ooarona'rmnor new mnsmr DISTILL A'IION PROCESS Application filed February 18, 1928.Serial No. 618,772.

which is to be treated by the process described in this application willbe referred to as tar and it will be understood that the term .coal .taras used in the claims herein is intended to include coal tar as-well ascoal tar m pitch obtained from the partial distillation of coal tar.

, It has been bound that if coal tars are distilled in such a way thatthey are exposed to unusually'hi htemperatures,durin distillation, orare eated at the usual dlstillation temperatures for unusually longperiods of ,time, the total oil recoverable as distillate from them isless than usual, and also the residual pitch is of higher melting pointthan usual, after a given percentage of oil has been removed asdistillate.

The oils'removed as distillate are almost always of higher commercialvalue than the residual pitches, and it is therefore desirable to carryout the distillation in such a way that either the maximum total yieldof oil will be'attained, or the highest possible percentage of oil willbe removed before any given commercial grade of pitch has been formed.

The use of tube stills, such for example as is disclosed on pages 485,486, et seq. of the fifth edition, Part I, of Coal Tar and Ammonia, byGeo. Lunge, Ph. D., published by The D. Van Nostrand Company, 1916,wherein the tar is heated as it passes continuously through a series oftubes, and is finally (lischarged into a chamber where the oil vaporsand pitch residue separate, has been found to increase the totalremovable distillate, and also to give a pitch residue of lower meltingpoint on the removal of a'glven percentage of distillate, as comparedwith the use of the ordinary discontinuous method of distillation, wherea charge of tar is heated to boiling and the various oil's pass oversuccessively, in vaporform to a condenser. Since ap proximately the sametemperatures are attained in both processes it is supposed that thedifference in oil yields is due principally to the difference in thetime during which the tar is heated, which is commonly about ten hoursin the discontinuous method and less than one hour in the tube still.

Lowering the distillation temperatures, in the discontinuous method, by(a) carrying on the distillation under greatly reduced pressure mm. ofmercury, absolute pressure, or less), or (b) the rapid passage throughthe tar of a gas having no chemical action on it, has been found toproduce results practicalllly the same as those attained in the tube stiAccordingly, it might well have been sup posed that in any one of thethree above methods (tube still, reduced pressure, or passage of gas)approximately the optimum conditions had been reached, with regard tothe total oil yield attainable orthe oil yield attainable in themanufacture of any given pitch.

However, I have discovered that, in a tube still, (a) by a suificientlygreat further ro duction of the time during which the tar is heated,greatly increased yields of distillate oil can be obtained, in theproduction of a.

given commercial grade of pitch; (did (6) it, in addition to thusshortening the time, advantage be taken of the knownboilingpoint-lowering efiect of reduced pressure (by artificiallyreducing the pressure in the separating chamber), a total yield ofdistillate can be obtained which is far in excess of that other improvedmethods amounts to the equivalent of 35-15% of the tar used.

These results are accomplished by heating the tar as it passes throughone or more tubular paths or zones, and discharging it at substantiallyits maximum temperature into a chamber or zone of relatively largevolume and correspondingly low pressure compared with said heating zone;where the oil vapors separate fromthe residual pitch, the vapors passingon into a condensing system and the pitch flowing out continuously atthe bottom of the separating chamber. It is 1 important, however, thatthe time occupied by-the tar in traversing the heated tubes should bevery short. Since it would be very difiicult to measure or to calculatethe actual mean time taken by a particle of tar to traverse such anapparatus (because of the expansion due to rise of temperature, and thevaporization of oil taking place continuously during a considerable partof the travel), an indirect way of defining this length of timerelatively must be used, and this will consist in defining the ratio ofthe cubic contents of the tubing traversed to the volume of the tarpassing through it in unit time.

If the unit of volume be the cubic foot, and the unit of time be theminute, this ratio will indicate the mean time which would be occupiedby a particle of tar in passing through such a piece of apparatus. Thisratio for commercial tube stills is commonlyabout 60, but in the presentinvention it is not more than 10, and may be much less or in otherwords, the tar is passed through the heating tube or zone in amounts notless than onetenth of the cubical capacity of said heating tube or zoneper minute.

In order to reduce the ratio to such low values, particular attentionmust be paid to the manner of supplying heat. A low value of this ratiomeans that a comparatively large quantity of tar is being heated perminute in an apparatus of comparatively small volume capacity; and thisnecessitates an in.- tense and concentrated application of heat. Thisinvention is not limited to any particular method or means of supplyingheat to the' tubing through which the tar fiows, but in the accompanyingdrawing is illustrated a form of apparatus, in which the heat may besupplied to the tubing by means of a bath of molten metal or alloythrough which the tubing passes. The rapidity with which heat passesfrom a liquid to a metal in contact with it (as compared with therelatively slow passage of heat from a gas to a metal) permits arelatively large quantity of heat to pass per minute into the tube walls(and thence to the tar) without recourse to the very high temperaturesin proximity to the tubes which would be necessary in order to transferheat bath of molten metal or hot liquid metal, such as mercury, lead, orother metal of low melting point, in the tank 4. The metal in this tankmay be kept in the molten state by heat,- ing the same in any convenientway as, for

example, by flames impinging upon the bot-F tom of the tank 4 or bypassing hot products of combustion through pipes passing through tank 4.A pipe 5 leads from the coil 3 to a separator 6 for pitch and vaporwhich is provided with a baflle plate 7. The pitch settles 1 in thebottom of the separator 6 and passes through the pipe 8 into the pitchreceiver 9, from which it may be withdrawn through the valve,10. Thevaporized constituents pass. from the separator 6 through the pipe 11into the coil 12 in the condenser 13 where they are condensed and passedto the oil receiver 14 from. whence the oil may be removed upwardly andis heated by the heat transmitted from the molten metal while it is intransit through the coil 3. The amount of heat supplied will besuflicient to cause the desired amount :of distillation to take place.The rate at which the tar is passed through coil 3 will be maintained asindicated above so as to produce an increased yield of oil ordistillates in proportion to "the amount of pitch or. residue that isleft.

The following are two examples out of many others that might be given toillustrate how the process has actually been carried out.

(1) A yield of distillate of 58% by weight with a pitch residue havinga'melting point of 237 F. has been produced at atmospheric pressure inthe separating chamber, with a discharging temperature of about 810 F.,and a rate of tar flow of about 70% of the cubic capacity of the heatingtube, per

' minute.

a rate of tar flow of about 38% of the cubic 125- capacity of theheating tube per minute, the separating chamber being maintained at anabsolute pressure of 55 mm. of mercury.

In both of the above examples, a coke oven tar was used, which byordinary distillation 1-30 gives about' 35% by weight of distillate inproducing a pitch having a melting point of 237 F., and in an ordinarytube still or in the recirculated gas method gives about 46% in making apitch of the same melting point. It is not practical to make a pitchhaving a melting point of' 352 F. by either the ordinary still or theordinary tube still method because of danger of coking, but the highestyields customarily obtained from such a tar by these methods are about40% by the former and 58% by the latter in making a pitch of meltingpoint about 300 F.

claim: 1. The process of distilling coal tar which comprises passingsaid tar through a heated zone in amounts not less than one-tenth of thecubical capacity of said zone per minute, supplying heat to the tarwhile passing throughsaid zone at such a rate as to elevate it to atemperature sufiicient to cause about 58% at least of the tar tovolatilize at atmospheric pressure, and then discharging the tar thusheated into a zone of relatively low pressure with respect to thepressure of said heated zone, thereby effecting a separation of the oilcontent in vapor form from the pitch content of the tar.

2. The process of distilling coal tar which comprises passing said tarthrough a heated zone in amounts not less than one-tenth of the cubicalcapacity of said zone per minute, supplying heat to the tar whilepassing through said zone at such a rate as to elevate it to atemperature of about 740810 F. prior to its discharge therefrom, and

' then discharging the tarthus heated to a zone of relatively lowpressure with respect to the pressure of said heated zone, therebyeffecting a separation of from about 58% to about 7 5% of the oilcontent in vapor form from the pitch content of the tar.

3. The process of distilling coal tar which comprises passing said tarthrough a heated zone in amounts not less than one-tenth of the cubicalcapacity of said zone per minute,- supplying heat to the tar whilepassing through said zone at such a rate as to elevate it todistillation temperature prior to its discharge therefrom and thendischarging the tar thus heated into a zone maintained at a pressureless than atmospheric, thereby efiecting the separation of the oilcontent in vapor form from the pitch content of the tar.

4. In a process of distilling coal tar to recover volatile oilstherefrom and produce a itch residue, wherein the tar is heated to.

istillation temperature while confined in and flowing through a heatedzone and vaporization of the volatile oils is thereafter effected bydischarging the heated tar into a chamber of low pressure relative tothat of said heated zone, the improvement which comprises passing saidtar through said heated zone at an increased rate of fiow amounting tonot less than one-tenth of the cubical capacity of said zone per minute,and supplying heat to the tar while passing through said zone at a ratesuflicient to elevate it to distillation temperature prior to itsdischarge therefrom, whereby the time period to which the tar issubjected to heat in its passage through the zone is diminished therebylowering the extent'of thermal decomposition of the tar and increasinthe oilyield, and recoverin separately t e volatile oil content of thetar libera'ted in the vaporization chamber and the residual itch.

5. In a process 0 distilling coal tar to recover volatile oils therefromand produce a pitch residue, wherein the tar is heated to distillationtemperature while confined in and flowing through a tube andvaporization of the volatile oils is thereafter effected by dischargingthe heated tar into a chamber of low pressure relative to that of saidheating tube, the improvement which comprises passing said tar throughsaid tube at an increased rate of flow amounting to not less thanonetenth of the cubical capacity of said tube per 6. In a process ofdistilling coal tar to recover volatile oils therefrom and produce apitch residue, wherein the tar is heated to distillation temperaturewhile confined in and flowing through a tube and vaporization of thevolatile oils is thereafter effected by discharging the heated tar intoa chamber of low pressure relative to that of said heating tube, theimprovement which comprises passin said tar through said tube at anincrease rate of flow amounting to not less than one-third of thecubical capacity of said tube per ininute, and supplying heat to the tarwhile passing through said tube at a rate suflicient to elevate it todistillation temperature, prior to its discharge therefrom, whereby thetime period to which the tar is sub'ected to heat in "its passagethrough the tu eis diminished thereby lowering the extent of thermaldecomposition of the tar and increasing the oil yield, and recoveringseparately the volatile oil content of the tar recover volatile oilstherefrom and produce a pitch residue, wherein the tar is heated todistillation temperature while confined in and flowing through a tubeand vaporiza- 5 tion of the volatile oils is'thereafter efiected bydischarging the heated tar into a chamber of low pressure relative tothat of said heating tube, the improvement which comprises passing saidtar through-said tube at an increased rate of flow amounting toapproximately seven-tenths of the cubical capacity of said tube perminute, and supplying heat to the tar while passing through said tube ata rate suflicient to elevate it todistillation temperature prior to itsdischarge therefrom,

whereby the time period to whlch the tar is subjected to heat in itspassage through the tube is diminished thereby lowering the extent ofthermal decomposition of the tar and increasing the oil yield, andrecovering separately the volatile oil content of the tar liberated inthe vaporization chamber and the residual pitch.

In testimony whereof I aflix my signature.

'2'5 JOHN V. E. DIGKSO-N.

